Electrically conductive ceramics and their use in fiber charging apparatus

Abstract

A conductive ceramic composition is disclosed which consists essentially of alumina, chromia, and magnesia, and is suitable for use as target electrodes in electrostatic fiber charging applications. Ceramics are disclosed which have exhibit volume resistivities of 10 12 ohm-cm or less at 20° C., and have excellent electrical stability and superior mechanical properties; and an electrostatic charging apparatus is disclosed which employs a ceramic electronic conductor having a volume resistivity of from about 1×10 7 to 5×10 10 ohm-cm and a hardness of at least 5 GPa.

What is claimed is: 
     
       1. An apparatus for electrostatically charging a continuous fibrous material being forwarded in a path from a source to a collecting means including a charged ion gun and an opposed grounded target electrode positioned on opposite sides of said path between said source and said collecting means, wherein: said target electrode has a ceramic surface facing said ion gun, said ceramic surface being formed of a stable electronic conductor comprising a polycrystalline, solid solution alumina-based ceramic composition having a volume resistivity of from about 1×10 7  to 5×10 10  ohm-cm measured at the operating temperature and a Vickers hardness of at least about 5 GPa.   
     
     
       2. The apparatus of claim 1 wherein the ceramic composition has a Vickers hardness of at least about 14 GPa. 
     
     
       3. The apparatus of claim 1 wherein the ceramic composition consists essentially of oxides of Mg 2+ , Cr 3+   and Al 3+ , wherein the atomic ratio of Cr 3+   to Al 3+   is within the range of from about 1000 to about 100,000 ppm, and the atomic ratio of Mg 2+   to Al 3+   is within the range of from about 25 ppm to 10,000 ppm.